Adjustable vascular ring and implantable kit comprising such a ring

ABSTRACT

Ring comprising:
         an outer belt ( 3 ) equipped with closing means ( 7 ) for closing the ring ( 1 ) around a duct ( 2 );   an inner chamber ( 4 ) that can be inflated and deflated;   a flexible inflation/deflation tube ( 5 );
 
wherein the lips have contact surfaces facing each other, the closing means comprising at least one perforation arranged on the contact surface of a first of the two lips and at least one protrusion protruding from the contact surface of a second of the two lips, the protrusion and the perforation being configured so that the protrusion is retained in the perforation by fitting, the fitting being selected to be released in the event of overpressure in the ring.

TECHNICAL FIELD

The field of the invention is that of medical devices that can beimplanted by surgical route around a biological duct, in particular avessel and more particularly a blood vessel such as the portal vein, inorder to allow adjustment of the diameter of the duct and therefore ofthe flow rate of a fluid (blood) capable of circulating therein.

These implantable medical devices are more precisely vascular rings thatcan be inflated and deflated using a fluid, so as to adjust their innerdiameter and thus the inner diameter of the ducts/vessels around whichthey are intended to be implanted.

The invention also relates to the kit that can be implanted by surgicalroute and allow control of the inner diameter of a vessel and, as aresult, the flow rate of a fluid circulating therein.

TECHNOLOGICAL BACKGROUND OF THE INVENTION

It is known to implant medical devices constituted by inflating bandingrings, around blood vessels of patients in order to restrict blood flow,for example on the pulmonary arteries. This is the subject of the patentapplication US2008/0097947A which discloses an annular banding devicefor the pulmonary artery, comprising an inflating banding ring intendedto be put in place around the pulmonary artery of the patient, aninflation tube connecting the banding ring to an insufflating button.The banding ring is generally C-shaped and comprises an external thinrigid silicone layer and an internal thin silicone layer, forming aninflating balloon. The rigid silicone external layer or wall extendsinto the end zone corresponding to the opening of the “C” so as to formlocking means making it possible to adapt the inflation bandage deviceto the diameter of the pulmonary artery. The ring also comprises holesfor the passage of sutures allowing it to be fixed to the pulmonaryartery of the patient. The inflation of this ring leads to thedeformation of the thin flexible silicone inside wall in a centripetaldirection, which causes a compression of the pulmonary artery and areduction in its inner diameter. The inflation is carried out using aliquid which is injected using the insufflating button which can also bepulled to allow deflation of the ring.

This type of inflatable vascular ring exists not only in cardiac surgerybut also in hepatic surgery. Thus the PCT application WO2010/102661Adescribes an implant for controlling the blood flow inside a vessel,namely more precisely the portal vein. This control is particularlycritical for the success of liver transplants and major hepatectomies.In fact, it is vital for the patient that blood flow in the portal veinjust after the transplantation or hepatectomy is not excessive, at therisk of unacceptably damaging the hepatic graft. This phenomenon isknown by the name of “Small For Size (SFS)” syndrome. This syndromeoccurs in the case of a portal flow rate greater than 260 ml/min per 100g of liver and/or a portal pressure greater than 20 mm Hg. It causes alethal alteration of the liver.

The perivascular adjustable implant according to WO2010/102661Acomprises an inflatable balloon of open annular shape, arranged inside anon-extendible band. The inflation balloon is connected to an injectionchamber by an inflation tube. The non-extendible outer band is equippedwith locking means of the ring or vessel. The inflation and thedeflation of the annular inner balloon makes it possible to restrict(inflation) or increase (deflation) the inner diameter of the vesselaround which the implant is placed. This implant comprises, on theinside of the inflatable balloon, means for measuring the blood pressureinside the vessel. FIGS. 2A to 2D of WO2010/102661A show the change inshape of the inflatable balloon as it is inflated. It appears that theinner wall of the inflatable balloon changes from a circular shape (FIG.2A) to a shape leaving a passage by growing, which is caused by a bulgein the inflation balloon. It is clear that such a compression of theportal vein is equivalent to crushing, causing a stenosis which leads toturbulences in the blood flow resulting in risks of thrombosis.

This implant according to WO2010/102661A does not therefore allowsatisfactory control of the flow rate and/or of the blood pressureinside the vessels, in particular the portal vein. This implant does notprovide an effective solution to the problem of SFS syndrome, after ahepatectomy or a liver transplant.

In addition, known implant medical devices require an additional surgeryto be removed from the patient.

OBJECTIVES OF THE INVENTION

In this context, the invention proposes a device for controlling thecirculation flow rate of a fluid inside a biological duct so as toregulate the flow rate or the blood pressure, which device can beremoved in a simple and safe manner.

BRIEF DESCRIPTION OF THE INVENTION

The invention concerns a ring with an adjustable inner diameter,intended to be implanted and closed around a biological duct, preferablya vessel, in order to control the diameter of this duct and thus theflow rate and/or pressure of a fluid circulating in the duct, the ringcomprising:

-   -   an outer belt with a constant diameter in a closed position;    -   an inner chamber that can be inflated and deflated in the closed        position, so as to vary its inner diameter;    -   a flexible inflation/deflation tube one end of which is        connected to the inner chamber and the other end of which is        intended to be connected to inflation means;    -   the outer belt and the inner chamber forming open collars, the        outer belt being equipped with closing means for closing the        ring around the duct;        wherein the closing means comprise two lips capable of being        joined to one another and to be separated from one another,        after the ring is implanted and closed around a biological duct,        by over-inflation of the inner chamber,        wherein the lips have contact surfaces facing each other, the        closing means comprising at least one perforation arranged on        the contact surface of a first of the two lips and at least one        protrusion protruding from the contact surface of a second of        the two lips, the protrusion and the perforation being        configured so that the protrusion is retained in the perforation        by fitting, the fitting being selected to be released in the        event of overpressure in the ring.

Thanks to these provisions the ring can be easily and rapidly removedfrom the biological ducts by a mere over-pressure. Over-pressure may beimparted to the inner chamber through the inflation/deflation tube oncethe treatment the tube is intended for is over.

However, over-pressure may also result in over-pressure within thebiological duct. Opening of the ring under such circumstance may improvethe safety of the patient.

The inner chamber, at rest and in the closed position, may have areduced inner diameter corresponding to the smallest reduced diameterrequired when in use for controlling the diameter of the duct.

These provisions add a pre-strain to the closing means facilitating itsopening upon over-pressure.

The ring according to the invention is a remarkable development of theknown implantable perivascular rings intended for controlling the bloodflow rate, in particular the portal flow rate and/or pressure.

Due to its original structure, this ring proposes a novel type ofnon-traumatic pneumatic or hydraulic modulation of the flow rate orpressure of the fluid, for example the blood, circulating in the duct,for example a vessel.

This constitutes significant progress towards successful hepatectomiesand liver transplants, by offering the practitioner an effective meansof combating SFS syndrome.

This ring is moreover secure, reliable, of a reasonable cost and capableof being produced on an industrial scale in compliance with the requiredquality and productivity standards.

The invention also relates a kit that can be implanted by surgicalroute, for controlling the flow rate or blood pressure, comprising thisring and an inflation/deflation module intended to be connected to theproximal end of the inflation/deflation tube, in order to allow the insitu injection of an inflation/deflation fluid into the inner chamber orthe in situ extraction of an inflation/deflation fluid out of the innerchamber.

Definitions

In the present disclosure, each singular and each plural interchangeablyrefers to a plural or a singular.

The definitions which are given below by way of examples, are intendedto facilitate the interpretation of the present disclosure.

“duct” and “vessel” interchangeably refer to a channel in which abiological fluid circulates, for example blood or lymph.

“closed position” of the ring means that the two ends of the ring arefixed to each other, so that the ring defines a cylinder.

The “at rest” state of the ring means that the pressures inside andoutside the inner chamber of the ring are balanced at the ambientatmospheric pressure. When the ring is positioned and closed around theduct, at rest, it is at least partially inflated so that it restrictsthe diameter of the duct, compresses it and reduces it.

The distal end of the flexible tube is its free end situated outside thebody of the patient in whom the implant is put in place, i.e. the freeend intended to be connected to the inflation/deflation means.

The proximal end of the flexible tube is the end opposite to its distalend, i.e. the end connected to the ring according to the invention.

By hardness D1, D2, is meant the Shore A hardness of the material(s)constituting the ring.

By the smallest reduced diameter required when in use for controllingthe diameter of the duct is meant the inner diameter of the innerchamber at rest, i.e. partially inflated, for which the diameter of theduct Dc, on which the ring is intended to be positioned, is restrictedand reduced to a minimal value Dcr with respect to the normal diameterDen (or maximum diameter) that the duct would have in a “normal state”without this ring around it. For each duct to be enclosed, the Dcr valuethat the duct must reach once the ring is positioned around it isdetermined. For example, if the duct is the portal vein, the smallestreduced diameter required when in use for controlling the diameter ofthe portal vein is the inner diameter Ø_(ir) of the inner chamber withwhich the diameter of the portal vein is restricted by 55%, preferably50% with respect to the natural, normal diameter Den of the portal veinwith no restriction. It must obviously be borne in mind that thediameter Dc of the duct can also be reduced if necessary, once the ringis positioned around it, by inflation of the inner chamber of the ringor increased by deflation of the inner chamber. By “normal state”, ismeant the state of the duct with no restriction and in which thebiological fluid circulates at a non-pathological, normal, averagebiological flow rate. In the normal state, the biological duct has anormal diameter Den, which depends on the biological species, sex andage of the individual.

The fact that the inner chamber, at rest and in the closed position, mayhave an inner diameter Ø_(ir) corresponding to the smallest reduceddiameter required when in use for controlling the diameter of the duct,makes it possible to define a shape of the inner chamber, with noinvagination, bulge or fold, in which the ring reduces, to a certainlevel, the diameter of the duct, and therefore the flow rate and/orpressure of the fluid circulating in the duct.

The smallest reduced diameter required for use can be defined by thelevel of reduction (e.g. expressed as a percentage of reduction) of thediameter of the duct around which the ring is intended to be implantedand locked. This percentage of reduction may correspond to therequirements for use. In particular, as regards the modulation of theflow rate and/or blood pressure, such as in the portal vein, it may beprovided that the ring has a Ø_(ir) selected in order to reduce by atthe most 55%, preferably by at the most 50%, the diameter of the vesselaround which the ring is intended to be arranged and locked. Thus, whenthe ring according to the invention is positioned and closed around theportal vein, at rest and therefore already partially inflated, the ringrestricts the diameter of the vein. It reduces this diameter by at themost 55%, preferably 50%. Depending on the requirement and desiredtreatment of the patient, it is then possible either to further inflatethe ring and thus further reduce the diameter of the inner chamber andas a result the diameter of the vein, or to deflate the ring andincrease the diameter of the inner chamber and as a consequence thediameter of the vein around which it is positioned.

The percentage reduction is adapted depending on the ducts around whichthe ring is intended to be put in place and also depending on the aim ofthe operation and of the positioning of such a ring. Thus, in the caseof SFS, it is desirable to reduce the diameter of the portal vein by 55%or even 50%. As a general rule, a human portal vein has a diameter of 15mm (±5 mm). The ring positioned and closed around the portal vein, in arest position, i.e. inflated (but not to its maximum) must reduce thediameter to 6.75 mm (±2.25 mm) for a 55% reduction of the diameter ofthe portal vein.

When the vessel is a vein (flexible wall), the diameter of the vessel isthat for which the flow rate of the circulating fluid corresponds to thenormal average biological flow rate.

In practice, during a hepatectomy or a liver transplant, the surgeonputs the open ring according to the invention in place around the portalvein, upstream of the liver, and closes this ring by firmly fixing itsends to each other. The portal vein is thus restricted so that itsdiameter is reduced by at the most 55%, preferably by at the most 50%.The portal diameter considered is, for example, that corresponding tothe normal average portal flow rate in humans, namely 700 ml (+/−200 ml)per minute, i.e. approximately 50 ml/min per 100 g of liver, in ahealthy individual; or also approximately 260 ml/min per 100 g of liver,in a patient having undergone a major hepatectomy (80% of the liverremoved). This flow rate value of approximately 260 ml/min per 100 g ofliver corresponds to the maximal value, below which the patient isexposed to SFS syndrome.

The practitioner can choose, as a function of the clinical data at theirdisposal, to further reduce or to increase the portal diameter byinflation or deflation of the inner chamber, in order to fix the portalflow rate at a value that is desirable for the patient, by graduallybringing this value back to normal, whilst taking the patient's state ofhealth into account.

This procedure could be applied to other medical or non-medical species,for which the positioning of a perivascular ring is prescribed in orderto reduce and then optionally increase the intravascular flow rate.

The diameter of the biological duct may be reduced using the ringaccording to the invention, until the duct is obstructed (clamping ofthe duct).

Preferably, Ø_(i) decreases by inflation and increases by deflation.

The fact that the inner chamber of the ring is inflated at rest in theclosed position around the duct and, moreover, that its inner diameter adecreases by inflation and increases by deflation, makes it possible tosafely and reliably control the flow rate and/or the internal pressureof a fluid circulating in the biological duct/vessel around which thering is put in place in the closed position, limiting the associatedrisks of stenosis and thrombosis.

According to a notable feature of the invention, the ring ischaracterized in that the inner chamber forms no invagination (norfold), nor bulge and has a “substantially” circular inner shape, in theclosed position of the ring, when this inner chamber is inflated. By“substantially” circular is meant, within the meaning of the presentdisclosure, a closed plane curve, the points of which are at the samedistance from the centre with a tolerance of plus or minus 20%,preferably 10%, of Ø_(i).

As indicated above, the ring may be an open collar which can be definedby at least one of the following features:

-   -   (i) the inner chamber forms, at rest and in the non-closed        position of the ring, an open collar on an angular sector        between 1° and 5°;    -   (ii) the outer belt forms, at rest and in the non-closed        position of the ring, an open collar over an angular sector        between 1° and 10°.

These provisions may add a further pre-strain to the closing meansfacilitating its opening upon over-pressure.

In the preferred embodiment, the open collar has no angular sector but anarrow channel, the ends to be joined in order to close the ring beingparallel when the ring is in open position at rest.

In one possible version of the invention, the flexible inflation tubecomprises at least one non-return valve.

In order to allow it to be visible to X-rays, it may be useful,according to the invention, for the ring to comprise at least oneradio-opaque part, for example a radio-opaque insert.

DETAILED DESCRIPTION OF THE INVENTION

The following description of a preferred embodiment of the ringaccording to the invention, will highlight other remarkable features.

This detailed description is given with reference to the attachedfigures in which:

FIGS. 1A & 1B represent perspective views of the ring according to anembodiment, deflated and in the closed and open positions respectively.

FIGS. 2A, 2B & 2C represent top views of the ring, at rest andrespectively in closed (2A) and open positions according to a preferredembodiment (FIG. 2C) and according to an embodiment variant (FIG. 2C),ready to be positioned around the duct.

FIG. 3 is a longitudinal cross-sectional view along the cutting planeIII-III of FIG. 2A, 2B or 2C.

FIGS. 4A & 4B are front views of the ring shown in FIGS. 2A & 2B or 2Crespectively.

FIG. 4C is a longitudinal cross-sectional view along the cutting planeIV-IV of FIG. 3 ,

FIGS. 5 a and 5 b are top views of another embodiment of the ring withclosing means capable of being separated from one another, after thering is implanted and closed around a biological duct, by over-inflationof the inner chamber, lips of closing means being joined to one anotherby a tongue attached to one of the lips and friction fitted in a throughhole of the other lip,

FIG. 5 c is a top view of another embodiment of the ring with closingmeans capable of being separated from one another, after the ring isimplanted and closed around a biological duct, by over-inflation of theinner chamber, lips of closing means being joined to one another by atongue attached to one of the lips and snap fitted in a through hole ofthe other lip.

As shown in the attached figures the ring (1) according to the inventionis a ring that can be inflated and deflated so as to vary its innerdiameter (Ø_(i)) so as to be able to compress and release the segment ofbiological duct for example of blood vessel such as the portal vein,around which said ring (1) is intended to be implanted and closed forcontrolling the flow circulating in the duct/vessel (2) represented bydot-and-dash lines in the figures.

The ring (1) comprises:

-   -   an outer belt (3);    -   an inner chamber (4) that can be inflated and deflated;    -   a flexible inflation/deflation tube (5).

The outer belt (3) has a substantially constant inner diameter and outerdiameter. This outer belt (3) is similar to an open collar (FIGS. 1B,2B, 2C & 4B) the 2 free ends of which have closing means (7) comprisingtwo outer lips (3 ₁, 3 ₂) extending in the centrifugal direction andhaving faces (3 ₃, 3 ₄) opposite one another in the open collar (FIGS.1B, 2B, 2C & 4B) and in contact with one another in the closed collar(FIGS. 1A, 2A & 4A). As shown in FIGS. 2A, 2B, 2C and 3 . These lips (3₁, 3 ₂) each comprise closing means described in greater details laterin order to ensure the closing (FIGS. 1A, 2A & 4A) of the ring (I) afterimplantation around the vessel (2) the flow rate of which is to beregulated.

This outer belt (3) is made of a semi-rigid material of hardness D1 andselected from the group of biocompatible elastomers, comprising or, evenbetter, constituted by silicone elastomers or analogues.

The inner chamber (4) is an inflatable and deflatable balloon having, atrest and in the closed position (FIG. 2A), a diameter (Ø_(ir)), whichmay correspond to the minimum diameter value (+/−10%) desired for use,namely a diameter which restricts the diameter Dc of the duct aroundwhich it is positioned as soon as it is put in place. In the case of thehuman portal vein, the normal diameter or maximum value D_(vpn) beforereduction is, for example, comprised between 10 mm and 20 mm. The ringput in place and locked around the portal vein has an inner diameterØ_(ir), which determines a reduction of the portal flow rate preferablyby at the most 50%.

Under the effect of the inflation, the inner chamber (4) increases involume in a centripetal direction, which reduces its inner diameterØ_(i). The deflation produces a reduction in the volume of the innerchamber (4), in centrifugal direction, in order to compress or releaserespectively the vessel (2) of a patient (e.g. portal vein), aroundwhich the ring (1) is put in place and closed using the closing means(7).

In the embodiment shown in FIG. 2B, the open collar constituted by theouter belt (3) has an opening extending along a narrow channel delimitedby the parallel faces 3 ₃ and 3 ₄ of the outer lips 3 ₁ & 3 ₂.

In the preferred embodiment variant shown in FIG. 2C, the open collarconstituted by the outer belt (3) has an opening extending over anangular sector α₃ comprised between 1° and 10° and preferably equal toapproximately 10° in this example. In this variant, the inner chamber(4) is an open collar the ends of which delimit an opening extendingover an angular sector c comprised between 1° and 5° and preferablyequal to approximately 5°.

As shown by the figures, in particular FIG. 3 , this inner chamber (4)is annular and comprises, in the example shown in the drawings (FIG. 3), an outer wall (4 ₁) in contact with and/or firmly fixed to the outerbelt (3) and a curved inner wall (4 ₂), the outer wall (4 ₁) and theinner wall (4 ₂) being connected to one another by lateral faces thatare substantially straight in the example selected, but which could becurved and are denoted by the reference numbers (4 ₃, 4 ₄). The innerchamber (4) could be toroid-shaped according to a variant.

The inner wall (4 ₂) forms the inner edge of this inner chamber (4).This inner edge (4 ₂) has a circular shape, when the ring is at rest(neither inflated: no internal overpressure, nor deflated: no internallow pressure) in the closed position (FIGS. 1A, 2A & 4A), and notarranged around a duct. According to the invention, this circular shapeof the inner edge (4 ₂), and, more generally, of the inner chamber (4)is maintained once the ring is arranged around a duct (e.g. vein) andduring the inflation and deflation operations. This means that the innerchamber (4) forms no invagination, fold or bulge, either in the reststate, in the inflated state, or in the deflated state. The shape of theinner edge (4 ₂) and, more generally, of the inner chamber (4), remains“substantially” flat and circular, once the ring is arranged around aduct (e.g. vein), from the inflated rest state to a further inflatedstate and a deflated state corresponding to the requirements of use. Inthe case of adjustment of the human portal flow rate, these inflated anddeflated states are included, for example, within the following innerdiameter Ø_(i) limits (in mm and in increasing order of preference):[5-25]; [6-24]; [7-20].

As shown in FIGS. 2A, 2B, 2C, 3, 4C, a radio-opaque band (4′) may beinserted between the inner chamber (4) and the outer belt (3), in theouter wall (4 ₂).

The inner chamber (4) is, for example, made of a flexible material ofhardness D2 and selected from the group of biocompatible flexibleelastomers comprising or, even better, constituted by siliconeelastomers or analogues.

According to a preferred feature of the invention, the hardness D1 ofthe outer belt (3) is greater than the hardness D2 of the inner chamber(4). For example, D1 is comprised between 60 and 100, preferably 70-90,for example of the order of 80 Shore A. According to another preferredfeature of the invention, the hardness D2 of the inner belt (4) iscomprised between 5 and 40, preferably 10 and 30, and even morepreferably of the order of 20 Shore A.

The flexible inflation/deflation tube (5) is connected by its proximalend (5 p) to the inside of the inner chamber (4) and by its distal end(5 d) to inflation means not shown in FIG. 3 . The inflation/deflationtube (5) is diametrically opposite the opening of the ring (1) as can beseen in FIGS. 1A, 1B, 2A, 2B, 2C, 3 and 4C. The outer belt (3) has anend piece (6) which extends towards the outside and which receives theproximal end (5 p) of the inflation tube (5). This inflation tube (5)can be equipped with a plastic non-return valve.

The inflation tube (5) can be made of the same material as the innerchamber (4), for example, with a hardness D3 comprised between D1 andD2, e.g. of the order of 60 Shore A.

The inflation/deflation means (not shown in the drawings) areconstituted for example by a syringe, preferably a screw syringe makingit possible to make precise inflation/deflation adjustments byinjection/tapping of the inflation/deflation fluid.

The ring (1) according to the invention can be put in place around thevessel (2) by the standard surgical route (laparotomy) or by thecoelioscopic route. The closing of the ring (1) is carried out byclosing means (7). The ring (1) thus positioned has a reduced innerdiameter (Ø_(ir)) which restricts the vessel (2) to the smallest reduceddiameter required for use (Dvpr) and thus limits the flow rate orpressure, for example blood, to a given level dependent on Ø_(ir). Thepractitioner then proceeds to adjust the flow rate and/or pressure, byinflation/deflation. In the case of hepatectomy or liver transplant,this adjustment aims to maintain an intrahepatic pressure less than orequal to 20 mm Hg, preferably 15 mm Hg. Ø_(i) is gradually increased bydeflation. D_(vp) and with it the flow rate and/or the blood pressure inthe portal vein therefore also increase(s) gradually, until D_(vp)reaches D_(vpn) (normal diameter or maximum diameter of the portalvein). The time taken for this rise of D_(vpr) to D_(vpn) is that whichis necessary for hepatic parenchyma in order to recover a capacity tocontain the intrahepatic pressure below 20 mm Hg, preferably below 15 mmHg, for the pressure and/or the flow rate downstream of the ring,corresponding to a portal diameter equal to D_(vpn).

This significantly limits the risks of SFS syndrome for the patient.

The ring according to the invention, once closed by the closing means,can be reopened by over-inflation of the inner chamber, which causes theclosing means to be spaced apart from each other. After opening the ring(1), the practitioner can also take advantage of the over-inflation ofthe ring (1), in order to keep the free ends of the ring (1) apart fromeach other and thus facilitate its extraction. This has the advantage ofavoiding further anaesthesia and its associated risks.

FIGS. 5A, 5B and 5C show embodiments of the ring according to theinvention wherein the lips of the closing means are capable of beingseparated from one another, after the ring is implanted and closedaround a biological duct, by over-inflation of the inner chamber.

In the embodiment illustrated on FIGS. 5A and 5B, the closing meanscomprise one perforation 3 ₅′ arranged on the face 3 ₃, forming acontact surface, of a first 3 ₁ of the lips and one protrusion 8protruding from the face 3 ₄, forming a contact surface, of a second 3 ₂of the lips. In particular, the perforation 3 ₅′ is a through hole, forexample of circular cross-section, formed in the first lip 3 ₁ and theprotrusion 8 is a tongue extending from the contact surface 3 ₄ of thesecond lip 3 ₂. As previously mentioned, the first 3 ₁ and second 3 ₂lips are formed of deformable material, and especially elastomericmaterial, such as silicone. The tongue is made in one piece with thesecond lip 3 ₂ so as to be elastically deformable. The tongue is forexample cylindrical of circular cross-section and has a length measuredperpendicularly to the second lip 3 ₂ from which it extends. The tonguecomprise a fitting portion 8 a attached to the contact surface face 3 ₄of the second lip 3 ₂ and sized, in terms of diameter and length, to beretained in the through hole of the first lip 3 ₁ by friction fitting.The friction fitting resulting from the combination of sizes andmaterial is selected to be released in the event of overpressure in thering.

The tongue is also provided with an extension adjacent the fittingportion 8 a opposite the second lip 3 ₂. The extension has a conicalshape with a diameter reducing from the base adjacent the fittingportion 8 a to a tip. The extension provides an extra-length able topass through the perforation 3 ₅′ and thereby forms a grasping portion 8b enabling the used to grasp the tongue so as to pull the fittingportion 8 a within the perforation 3 ₅′.

The tongue and the through hole could have any other suitable crosssection, preferably complementary to one another.

The embodiment illustrated on FIG. 5C differs from that of FIGS. 5A and5B in that the tongue 8′ comprises an enlarged portion 8 a′ sized torest on a surface of the first lip 3 ₁ opposite the contact face of thefirst lip 3 ₁ when the ring is closed, thereby providing a snap-fitting.The enlarged portion has a transverse dimension greater than that of thethrough hole and, in particular, a transverse dimension that is 5% to20% greater than that of the through hole. In the illustratedembodiment, the fitting portion of the tongue 8′ attached to the contactsurface of the second lip 3 ₂ is narrower that the through hole of thefirst lip 3 ₁. The fitting portion may then be arranged within in thethrough hole without contacting walls of the through hole. However, thefitting portion could be otherwise configured so as to provide afriction fitting with the through hole.

As in the embodiment of FIGS. 5A and 5B, the tongue 8′ may comprise agrasping portion adjacent the fitting portion opposite the second lip 3₂.

The invention is not limited to the disclosed tongues and through holes.The closing means could comprise any other kind of protrusion andperforation configured so that the protrusion is retained in theperforation by fitting such as force fitting, friction fitting, snapfitting and others, the fitting being selected to be released in theevent of overpressure in the ring.

The invention claimed is:
 1. A ring with an adjustable inner diameter,intended to be implanted and closed around a biological duct, in orderto control a diameter of the biological duct and thus a flow rate and/orpressure of a fluid circulating in the biological duct, this ringcomprising: an outer belt with a constant diameter in a closed position;an inner chamber that can be inflated and deflated in the closedposition, so as to vary an inner diameter thereof; a flexibleinflation/deflation tube, one end of which is connected to the innerchamber and the other end of which is intended to be connected toinflation means; the outer belt and the inner chamber forming opencollars, the outer belt being equipped with closing means for closingthe ring around the biological duct; wherein the closing means comprisetwo lips capable of being joined to one another and to be separated fromone another, after the ring is implanted and closed around thebiological duct, by over-inflation of the inner chamber, wherein thelips have contact surfaces facing each other, the closing meanscomprising at least one perforation arranged on the contact surface of afirst of the two lips and at least one protrusion protruding from thecontact surface of a second of the two lips, the protrusion and the atleast one perforation being configured so that the protrusion isretained in the at least one perforation by fitting, the fitting beingselected to be released in the event of overpressure in the ring.
 2. Thering according to claim 1, wherein the inner chamber, at rest and in theclosed position, has a reduced inner diameter corresponding to asmallest reduced diameter required when in use for controlling thediameter of the biological duct.
 3. The ring according to claim 1,wherein the at least one perforation is a through hole formed in thefirst lip and the protrusion is a tongue comprising a fitting portionattached to the contact surface of the second lip and sized to beretained in the through hole by friction fitting.
 4. The ring accordingto claim 3, wherein the tongue comprises a grasping portion adjacent thefitting portion opposite the second lip, the grasping portion beingsized to pass through the through hole and to be grasped by a user. 5.The ring according to claim 1, wherein the at least one perforation is athrough hole formed in the first lip and the protrusion is a tongue, thetongue comprising a fitting portion attached to the contact surface ofthe second lip and sized to be arranged within the through hole, and anenlarged portion sized to rest on a surface of the first lip opposite acontact face of the first lip.
 6. The ring according to claim 5, whereinthe tongue comprises a grasping portion adjacent the fitting portionopposite the second lip, the grasping portion being sized to passthrough the through hole and to be grasped by a user.
 7. The ringaccording to claim 1, wherein the inner chamber has no invagination atrest and, in the closed position of the ring, an inner edge of the innerchamber intended to be in contact with the duct has a substantiallycircular shape.
 8. The ring according to claim 1, wherein the innerdiameter of the inner chamber decreases by inflation and increases bydeflation.
 9. The ring according to claim 1, wherein the lips extend inthe centrifugal direction.
 10. The ring according to claim 1, comprisingat least one radio-opaque part.
 11. The ring according to claim 1,wherein the inner chamber forms, at rest and in a non-closed position ofthe ring, an open collar on an angular sector less than or equal to 5°and the outer belt forms, at rest and in the non-closed position of thering, an open collar over an angular sector less than or equal to 10°.12. A kit that can be implanted by surgical route, allowing anadjustment of an inner diameter of a biological duct and thus a flowrate of a fluid circulating in the biological duct, the kitcomprising: * a ring according to claim 1; * an inflation/deflationmodule intended to be connected to a distal end of the flexibleinflation/deflation tube, in order to allow the in situ injection of aninflation/deflation fluid into the inner chamber or the in situextraction of an inflation/deflation fluid out of the inner chamber.